Earth Observation (EO): How Optical Components Help Monitor Our Planet

Earth Observation (EO) is having its moment, and it’s easy to see why. For the military, it offers a bird’s-eye perspective of surroundings and opens the door for quick disaster response. When it comes to sustainable development goals, it’s helping us to keep track of one of the biggest challenges of our age – climate change. And, in communications, it helps us to establish the infrastructure that keeps us connected. But there’s so much more to EO, and optics play a huge role.

What is Earth Observation (EO)?

Let’s break it down. Earth Observation, or EO, concentrates on gathering and analysing information about the world we live in to serve specific needs. This is facilitated by Earth-Observation satellites – of which 1460 were launched between 2002 and 2022.

How Do Earth-Observation Satellites Work?

The technology onboard EO satellites varies depending on each mission. Some, like RADARSAT-2, use microwave radar tech to support purposes ranging from ice studies to coastal examining. Others, such as CryoSat-2, lean on radar altimetry to measure changes in Earth’s ice cover. Meanwhile, sats like Sentinel-2 – a member of the EU’s Copernicus programme – are armed with optical payloads to capture detailed multispectral imagery.

High-resolution satellite image of Hong Kong City, China, based on Copernicus Sentinel-2 imagery from 2019

Labelled as the largest EO strategy in the globe, Copernicus monitors our planet on a global scale for ecological and climate impact using a set of purpose-built satellites, all supplied with tailored payloads. Sentinel-2 is a fundamental aspect of the fleet, comprising a constellation of three identical satellites in the same orbit – all with a big emphasis on optics.

Optical Components for Earth Observation (EO) Satellites

As optical imaging satellites, each Sentinel-2 unit integrates fine-tuned optical components in their Multispectral Instruments (MSI). Optics such as Mirrors, Beamsplitters, and Diffusers fulfil important roles here.

At the centre of the MSI, a three-mirror anastigmat (TMA) telescope collects and focuses light, while a beamsplitter separates visible and near-infrared (VNIR) light from short-wave infrared (SWIR) bands. Additionally, a diffuser is employed for radiometric calibration, guaranteeing consistent and accurate measurements throughout the mission.

Earth Observation for Agriculture

Sentinel-2 isn’t just used for assessing emergency management and climate monitoring, however. It’s also being used in agribusiness for precision farming, and there’s high demand for it worldwide.

Leveraging metrics from satellites, just like Sentinel-2, the Australia-New Zealand Collaborative Space Programme has awarded funding to EO initiatives aimed at understanding and managing fire-prone landscapes, promoting resilient land use, boosting soil moisture measurements, and backing crop cultivation.

In Europe, the EU has also switched on to the agri benefits of EO insights, augmenting its capability with artificial intelligence (AI) and on-field tech to revolutionise precision farming. The recent EU-funded AgriBIT project combined the high-tech solutions in pilot projects – spanning vineyards in Italy, tomato production in Portugal, and peach orchards in Greece – enabling near-real-time inspection of crop health, pest infestations, and bacterial infections for optimal harvesting.

And the momentum continues. The UK Government has recognised the transformative opportunities of EO and invested heavily in the domain, too. Through its association with the Copernicus venture, EO has been prioritised throughout multiple UK governmental departments – including agriculture-related areas of use for the Department for Environment, Food, and Rural Affairs (Defra) – underlining its strategic importance.

Of course, agricultural monitoring is a valuable part of EO. Yet, a priority for these spaceborne platforms does focus on tracking environmental shifts and the impacts of global warming. Recently, the European Space Agency (ESA) and NASA united to boost the potential of EO for climate change investigation even further. Their alliance involves two satellites working together – and it even encompasses lasers.

Laser-Based EO Satellites

The ESA’s CryoSat-2, Europe’s first-ever spacecraft committed to studying ice, and NASA’s ICESat-2, equipped with an Advanced Topographic Laser Altimeter System (ATLAS), have joined forces for a groundbreaking collaboration. Known as CRYO2ICE, this first-of-its-kind campaign brings together CryoSat-2’s radar altimetry with the laser-based accuracy of ICESat-2. By combining two missions, this fusion enables both radar and LiDAR readings of the same ice almost simultaneously. This allows scientists to calculate snow depth on land and sea, improving the credibility of sea ice thickness and ice-sheet elevation data.

NASA-generated image of the ICESat-2 spacecraft. Courtesy of NASA: https://icesat-2.gsfc.nasa.gov/

ICESat-2’s laser device is engineered for exceptional accuracy. By splitting a single laser into six beams, it can measure Earth’s surface with remarkable detail. Operating at a wavelength of 532 nm, it includes a primary laser and a backup.

With this setup, ICESat-2 collects data every 2.3ft along its ground path. This is made possible by the optical bench within ATLAS that guides pulses of light through an intricate arrangement of lenses and mirrors before they are beamed toward Earth.

Key elements of ATLAS further refine the process. Beam-Shaping Optics control the beam’s divergence, making sure it covers the desired footprint. Meanwhile, a Diffractive Optical Element (DOE) splits the laser into the six beams, enhancing spatial resolution. Collectively, these leading-edge optical technologies enable ICESat-2 to complement CryoSat-2’s radar capabilities, creating a unified objective that sets a new standard in EO.

Commercial EO

It’s not just Government space agencies leading the charge in EO. Commercial companies like Maxar are also revolutionising the sphere with cutting-edge sats like WorldView-3. Exceeding its intended lifespan, it delivers high-resolution imagery for a wide range of applications, for example, mapping, environmental monitoring, urban planning, disaster response, and military reconnaissance.

Pivotal to the satellite is the WV-3 Imager, which features 29 spectral bands and incorporates a sophisticated configuration of SWIR sensors, optics, and a telescope with a primary mirror designed for high-clarity imaging. Supporting this is the secondary CAVIS (Clouds, Aerosols, Vapors, Ice, and Snow) Imager, equipped with standalone optics and a dedicated focal-plane package to enhance atmospheric correction.

Three-Mirror Anastigmat (TMA) Setups for EO Satellites

Detail and innovation are at the core of all EO sats, reflected in their cutting-edge optical blueprints, such as Three-Mirror Anastigmat (TMA) setups. These systems are specifically chosen because once satellites are launched, they can’t be easily adjusted like ground-based instruments. That’s why many EO sats – including Sentinel-2, Pléiades (a CNES environment-focused constellation), and GeoEye-1 – rely on this high-performing design.

TMA setups offer more than just endurance. By folding the light path, they allow for compact and lightweight designs – critical for space missions. Beyond practicality, they also excel in correcting three fundamental optical aberrations: Astigmatism, coma, and spherical aberration, ensuring sharp imaging across a wide field of view.

The Future of EO

With optical components at the heart of today’s EO operations and increasing investment fuelling the data they deliver across industries, the trajectory of EO is clear – it’s on the rise. If you’re in need of any of the optics mentioned here, reach out to our experts to explore how we can help elevate your mission.